1. Field of the Invention
The present invention relates to a plasma display panel (PDP) and, in particular, to display electrodes of the PDP.
2. Description of the Related Art
A plasma display panel (PDP) is generally a display device in which vacuum ultraviolet (VUV) rays from plasma generated by gas discharge excite phosphors to emit red, green, blue visible lights for producing an image. Such a PDP can achieve a large screen display with a size over 60 inches (˜152.4 cm) while keeping its thickness within 10 cm. As an emissive display device like a cathode ray tube, the PDP has features of excellent color reproduction and no distortion along viewing angle. Compared to a liquid crystal display (LCD) device, the PDP has an advantage of a simple manufacturing process resulting in a good productivity and low cost. As a result, the PDP has emerged as a promising flat display device for home and industry.
In a typical alternating current (AC) PDP, as shown in FIG. 5, address electrodes 103 are formed on a rear substrate 101 and extend in a first direction (y-direction) and spaced apart along a second direction (x-direction). A dielectric layer 105 is formed on the rear substrate 101 to cover the address electrodes 103. On top of the dielectric layer 105, barrier ribs 107 positioned between the address electrodes 103 are formed in a stripe pattern, and red (R), green (G) and blue (B) phosphor layers 109R, 109G, 109B are formed between the barrier ribs 107.
On a first surface of a front substrate 111 facing the rear substrate 101, formed along one direction crossing the address electrode are X and Y electrodes 113, 115, i.e., display electrodes, each including one of a pair of transparent electrodes 113a, 115a and one of a pair of bus electrodes 113b, 115b. A dielectric layer 117 and a MgO protective layer 119 in turn are formed on the entire front substrate 111 covering the X and Y electrodes 113, 115.
Discharge cells 121R, 121G, 121B are formed at locations where the address electrodes 103 of the rear substrate 101 cross a pair of the X and Y electrodes 113, 115 of the front substrate 111.
Such an AC PDP has millions of discharge cells arranged in a matrix pattern and adopts a driving method using memory characteristics to drive such a large number of discharge cells simultaneously.
As for the driving method, a voltage difference over a certain value is necessary to start a discharge between the X electrode 113 (a sustain electrode) and the Y electrode 115 (a scan electrode), both composing a pair of the display electrodes. A threshold voltage having the certain value is called a firing voltage (Vf). When an address voltage (Va) is applied between the Y electrode 115 and the address electrode 103, the discharge starts. The plasma is generated by the discharge in the discharge cell, and the electrons and ions in the plasma move toward the electrodes having the opposite polarity. As a result, the electrical current flows.
Since the dielectric layer 105 or 117 is coated on each electrode 103, 113, 115 of the AC PDP, most of the moving space charge is deposited on the dielectric layer 105 or 117 with the opposite polarity. Therefore, the net voltage difference across the gap between the Y electrode 115 and the address electrode 103 becomes smaller than the initial address voltage (Va), and that causes the discharge to be weak and disappear eventually. At this time, the dielectric layer 117 on the Y electrode collects a relatively large amount of the ions, compared to the dielectric layer 117 on the X electrode 113. The accumulated charges on the dielectric layer 117 over the X and Y electrodes 113, 115 are called the wall charge (Qw). Also, the voltage across the space between the X and Y electrodes 113, 115 is called the wall voltage (Vw).
For the case where a certain voltage (Vs; discharge sustain voltage) is applied between the X electrode 113 and the Y electrode 115 successively, the discharge starts in the discharge cell 121R, 121G, 121B when the sum (Vs+Vw) of the discharge sustain voltage (Vs) and the wall voltage (Vw) exceeds the firing voltage (Vf). The vacuum ultraviolet ray generated at this moment excites the corresponding phosphor layer 109R, 109G, 109B so that visible lights are emitted, and the transparent front substrate 111 transmits the visible light to show an image.
In the PDP with the barrier ribs 107 and the display electrodes 113, 115 formed in a stripe pattern as shown in FIG. 5, however, crosstalk may occur between one discharge cell and the neighboring cells 121R, 121G, 121B. Also, since the discharge space is open in the direction of the barrier rib, misdischarge may occur between the neighboring discharge cells 121R, 121G, 121B in the direction of the barrier rib. In order to prevent the misdischarge, the distance from the display electrode 113, 115 to that of the neighboring cells 121R, 121G, 121B in the direction (y-direction) of the barrier rib 107 is larger than a certain value. However, that hinders improving a luminous efficiency.
The U.S. Pat. No. 5,640,068 discloses a plasma display panel for solving the aforementioned problem. In addition to barrier ribs formed in a stripe pattern, its structure includes a pair of transparent electrodes of display electrodes formed, in each discharge cell, protruding from each bus electrode and facing each other. Even this structure may not prevent the misdischarge from happening in the direction along the barrier ribs.
A PDP with barrier ribs, formed in a matrix pattern by horizontal and vertical barrier ribs is provided to solve the problem as well as to enhance the luminous efficiency by increasing the phosphor area in each discharge cell. Further, in a PDP with partially modified barrier ribs in the structure, misdischarge in a non-discharge area may occur because bus electrodes of the display electrodes placed in the neighboring discharge cells are exposed to the non-discharge area. Thus, the misdischarge in the non-discharge area may cause the degradation in color purity due to a neon (Ne) light-discharge and in PDP efficiency due to unwanted power consumption.